System of electrical transmission and transformation



April 24, 1928.

P. H. THOMAS SYSTEK OF ELECTRICAL TRANSMISSION AND TRANSFORMATION Filed Aug.'7, 1925 2 Sheets-Sheet 1 INVENTOR WITNESSES: @M

April 24, 1928.

P. H. THOMAS SYSTEM OF ELECTRICAL TRANSMISSION ANN TRANSFORMATION Filed Aug. 7, 1925 2 Sheets-Sheet 2 Fig. 6'

INVENTOR W ITNESSES @Mflm Patented Apr. 24, 1928.

UNITED STATES l 1,667,087 PATENT OFFICE.

PERCY H. THOMAS, OF UPPER MONTCLAIB, NEW JERSEY.

SYSTEM ELECTRICAL TRANSMISSION AND TRANSFORMATION.

Application filed August 7. 1925. Serial- No. 48,796.

The present invention relates to im rovements in certain alternating current e ectric systems used to maintairra constant current or a constant voltage service and to means 5 for securing greater effectiveness and greater economy in such systems. 4

It has been known for some time that, if two branch circuits be connected across a supply circuit, each branch containing an inductance and a condenser in series, but alternating in sequence so that if the condenser is connected to one terminal of the supply in one branch circuit, a. reactance will be connected to this terminal in the other circuit, a consuming device connected between the intermediate connection points of the two branches will be supplied with a constant current, provided a constant potential is impressed by the supply circuit but will be supplied with a constant-potential if a constant current be impressed by the supply, provided the condenser and reactance are properly proportioned. Such a system has been used in practical service to supply constant current street lighting circuits.

My invention seeks to simplify such systems and render them more economical as well as more effective. It will be understood by reference to the appended drawings and the description thereo Figure 1 shows a simple embodiment of my invention, adapted to transform power at constant potential into power at constant current or vice versa' and Fig. 2, is a modification of detail. Figs. 1 and 1", show the vector relations of the voltages on'the several elements of the simple embodiment of my system. Figure 3 shows a development of Fig. 1, adapted to permit adjustment of the delivered voltage to the needs of the system and Fig. 4, is a modification of detail. Figure 5, is a more complete system adapted to transform power at constant potential to power at constant current and then to distribute it at constant current to a series of different points at each of which constant potential is obtained or vice versa. For example, such a system might be economically used to supply power from a substation to a number t widely scattered stations in a farming country, giving the advantages of normal constant potential service at each station and the economy of constant current transm ssion. Figure 6, shows my invention adapted to a three phase system, and Fig. 7, 1s a modification Where three phase power is transmitted over two wires. Figure B, shows a single phase, single wire embodiment of my system.

In Figure 1, 1 represents a. unit network or transforming unit, includinga reactance 2, a condenser 3, and an autocoil or transformer winding 4. The en ply, which in this case is a generator, is siiown at 5, and

the receiving circuit or load 6, is connected between the common point of the reactance 2 and the condenser 3, and an intermediate point of the winding 4. The connections of thcseelements are clearly shown in Fig. 1. The action may be explained as follows: If the current supplied by the generator 5, be constant current, that 15 current havingthe same strength regardless of the voltage, this current, less the small amount'taken to magnetize the auto-coil 4, must flow through the reactance 2 and the condenser 3 in series. Since the voltage on the reactance will be substantially opposite to the voltage on the condenser, the diagram of voltages will be appronimately as shown in'Fig. 1, assumin there is no load current taken. E and are respectively the voltage and current in the reactance,'E and I are the voltage and current in the condenser, E and I, the voltage and current in the load and E and 1,, 1n the generator. The phase and magnitude pf the receiving voltage E is shown in Fig.

If now a load current flows in the load 6, Fig. 1, this load divides in two parts, passing in opposite directions through the winding 4 and back through the condenser and the reactance. There is then in the reactance 2, in addition to the constant generator current, one half of the load current. This additional current changes the phase and magnitude of the current and volta e in the reactance 2, as shown in Fig. 1". gimilarly with the currents in" the condenser resulting in the voltages E and E,, Fig. 1. For this diagram to be strictly correct the reactance and condenser must be adjusted so as to take Assume thatthe impedance oi the react-- ance is represented by the complex quantity it, andthat of the condenser by h then it can be easily shown by the wellknown laws of the electric circuit that E.=[ 1-n h.-nh.1 a-aamha omha 1..

nil and (140E, represent the voltages respectively between the intermediate point of the auto coil 12 and the ends of the coil-the voltage all. being on the condenser side.

Also-= (Lam -ah If it be assumed that n=5 and that there are no losses in the condenser, reacta'nce or auto-coil and further 'be assumed that h =h these equations reduce to the following- 1: in a t It is thus proved that with these assumed limitations the load voltage E is entirely independent of the load current L, that is, E, will be a constant voltage as long as I is constant and h does not change. E is also removed 90 in phase from L.

Similarly the generator voltage E depends only on Land is thus proportional to the load, and the phase of E while displaced 90 from the phase of'l will advance or fall back by the same angle as the phase of L. In other words the power factor of the generator will be the same as that of the load,- but will be leading in one case and lagging in the other. This may be a matter of great importance for in transmitting power by such a system a lagging load power factor may mean leading power factor in the step-up and step-down transformers and in the line. Now if a constant potential, E,, be impressed on the unit network by the generator, the load current I will be constant in value, thus providing a source of constant current and the potential in the receiving circuit E will be dependent on the current int-he generator circuit or vice versa.

The relative phases of the quantities will be the same regardless of whether the constant current occurs in the receiving circuit or the sending circuit, which latter may be either the circuit of E or of E,.

In any actual installation there will be en'- ergy losses in reactances and condensers, although the latter will be small. Consequently the results will not be exactly as shown by the simple Equations 1 to 4 inx I elusive- The Equations 1 to 4 permit the determination of the effect of these losses. It will be well in using these equations for this purpose to write the complexquantity h as h '+jh and k as hJ-q'h, in the usual way, where h and k are energy loss quantities and 7a.- and it," are out-of-phase quantities.

In the Equations 1 to 4 no account is taken of the losses in the winding 4, but these will be small and will act approximately as part of the load. The magnetizing current of the winding Jr-determined by the voltage E,-must be combined with the generator current I and will be in quadrature when the load power factor is.1, and will tend to reduce the generator current as the load gets a lagging power factor. The effect of losses in reactance and condenser is to increase the voltage E and the current I somewhat and to advance the phase of the current I slightly.

The efiect of locating at one side of the middle, the intermediate point of the transformer winding at which the load circuit is connected is important. As may be seen by inspection of Equation 1 above, the efiect of making 1 less than is to add an E. M. F.

to E,. 'leading'by 90 when Land E are If L lags behind E as with a in phase. 7 lagging load power factor, this voltage due to the displacement of the intermediate point tends to increase E and thus acts as a compounding means for the voltage. tending to 'make up for any loss of potential due to other apparatus such as transformers. Similarly it may be seen from Equation 3, that L,may be compounded for the effect of L by varying n. By adjusting the position of I l t" the intermediate point of the auto-coil the amount of the compounding of the voltage at E or the current L. can be controlled. This is practically an important matter. It should be noted, however, that, due to the fact that the power factor may be leading in the transmission circuit and transformers feedin such aunit network as here describe the load current I may cause a rise in potential rather than a drop. If this rise should be excessive the compounding obtainable by varying the factor a may be made ne ative.

5 shown in Fig. 2, it will sometimes be 'adantageous to use a transformer, 7, with a for the compounding as described above for Fig. 3, shows a unit network similar in principle to Fig. 1, but arranged to give a range of load voltage without changing the voltage on the generator or on the condenser or the reactance and without changing any compounding that may be provided. This is often of advantage because there is usually a most favorable voltage for the design and construction of condensers which is too high or too low for the usual motor and lighting circuits. I accomplish this result by connectin the load 17, between an intermediate olnt 18, of the reactance winding 11, and an intermediate point 19 of the transformer winding 12. 13 represents the condenser and 14, shown dotted, is the position of the load as shown in Fig. 1, which may be called the normal position. The points of connection of the load 17, viz, 18 and 19, must be so chosen that the portion of the reactance between the load connection point 18, and the point 15, is approximately the same proportion of the whole reactance as the portion of the winding 12 between the load connection point 19 and the point 15 is of the portion of the winding 12 between point 15 and the point 16 or the normal point of connection. These points 18 and 19 may be called homologous points. The generator is shown at 5.

In case the point of connection 16 of the load 14, is in the middle of the winding 12, there is no compounding. In case it is displaced from the point 15 there is compounding, positive or negative according to the displacement, an increase in the potential E for a lagging load is secured by moving the point of connection of the load along the winding 12 toward the condenser and vice versa. The same amount of compounding is retained with a lower load voltage by connecting the load between the homologous points 18 and 19 as shown at 17.

In this operation the reactance 11 and the winding 12 act as auto-transformers and the eitect of the current in 17 on the network unit is the same as though a current appropriately less than the load current were taken at the normal load position.

If desired the point 15 may be grounded to protect the load from the relatively high potentials of the reactance and condenser.

Instead of using the reactance 11 and the winding 12 of Fig. 3, as auto-transformers, separate windings may be put on the same cores to supply't e load 17 as shown respectiyely at 11- and 12, Fig. 4. This arrangement has the advantage of making the load circuit electrically separate from the reactance and condenser circuit. If a transformer be used to adjust the condenser voltage to the network voltage an intermediate point of the secondary of this transformer or a separate winding may be used in co-operation with the winding 12 of Fig. 3, or with the secondary of the transformer 12 in Fig. 4, to secure the same modification of the load voltage. The primary of the windmg 12 may serve as an auto-transformer to receive the impressed voltage from the generator 5, as shown.

As already explainedthe nature of these circuits is such that the receiving circuit may be made a generator circuit and vice versa, and the supply may be made either constant current or constant potential giving respectively a constant potential or constant current work circuit.

Where desired these unit networks may be used to provide a constant current from a constant potential supply and this constant current utilized in a distribution system to produce local constant potential supplies. Such an arrangement is shown in Fig. 5, where 20 is a unit network with a source of constant potential 24, connected as shown. This will produce a constant current in the circuit 27 as already explained. Instead of delivering the current from the terminals and 26 where the reactance and condenser ar'e connected, the winding 21 may be extended as an auto-transformer and the current be delivered at 22 and 23 at a. higher voltage and with a correspondingly smaller current.

The compounding adjustment described in connection with Fig. 1, may be here used as also in the case of any of the other networks.

-The current from the unit net-work 20 passes to the distributing circuit 27 and through the local networks 28, 28 and 28. I have shown three such networks but there may be any desired number, more or less than three. I have shown transformers, 29, 29 and 29, as introducing the constant line current in the circuit 27 into the several local unit networks. Auto-transformers might be used if desired. The work circuits 30 30 and30 will each be impressed with a constant potential independent of the others and each independent of its load. The efiect of a heavy load in the work circuit 30 is to cause a high voltage at the primary terminals of the transformer 29 receiving the constant current from the unit network 20. Similarly with load in the unit networks 28 and 28 and their work circuits 30 and 30. The voltages in the primaries of all the transformers 29, 29 and 29 are summed up in the circuit 27 and with the various voltage losses added constitutes the voltage on the winding 21 of the unit network 20 and this in turn determines the current in the generator 24.

Any other constant current devlces may be used in place of the unit networks 28, 28 and 28, or any other source of constant current might be used in place of the unit) network 20. I v

If no current is taken by the work circuit 30*, for example, the voltage on the primary of its transformer 29", will drop to near zero. If, however, a short circuit occurs on the work circuit a very high voltage will occur 'at the transformer primary and precautions to limit such a rise of potential may be taken to advantage in some cases. However, the system is substantially protected because any undue increase in the voltage on the prlmary of the transformer 29 for example will cause a magnetic leakage between the two halves -of the secondary winding of this transformer which has the effect of reducing the maximum load current that can flow even on short circuit and limiting the rise in primary voltage. Furthermore, a large increase 1n voltage on a single local circuit is a much smaller relative increase in the system as a whole. A high voltage in the circuit 27 causes a large currentin the supply circuit 24. Additional protective means such as spark gaps may be used. Circuit breakers in the load circult opening on overload will be an added safeguard.

. The load circuit in each local unit network for example 28", is isolated from the constant current circuit 27 by the transformer 29 and may be independently grounded at will.

In Fig. 6 I have shown an arrangement similar to Fig. 5 but adapted to deliver three phase power. Each single phase circuit is similar to that of Fig. 5 or any of its possible modifications as far as the generator network and transmission line are concerned. Sources of currents in three phase relation are supplied at 31, 31 and 31. As shown, one end of each of the three constant current circuits are connected together at a common point 33 at the generating station in the well known manner to supply three phase line currents. The common point 33 may be grounded if desired as at 55. The three transformer secondaries 33*, 33 and 33, may also be connected in delta in the usual way. At any desired point local unit networks may then be utilized to produce local three phase constant potential work circuits.

As many of these separate local combinaooms? tions may be connected in the circuit as may be desired within the limits of the apparatus. Two shown.

In the network 50, the three reactance coils 45, 45 and 45 are wound on a single three legged core, thus giving a magnetic linkage which tends to balance the currents since the magnetic flux in any core leg must equal the resultant of the fluxes in the other cores, neglecting magnetic leakage. The condensers 46, 46" and 46 correspond to the condenser 3 of Fig. 1 and the transformer windings 47, 47 and 47, to the winding 4 of Fig. 1. The three phase constant potential bus bars are shown at 49 and the neutral point of the system at 48, obtained by connecting together the several load connection intermediate points of the windings 47 47 and 47. A typical'load isshown at 52, an induction motor being diagrammed.

The local unit network 51 contains a three typical networks, 59 and 51, are

phase core type step-down transformer 53.

However, only two of the line wires 32*, 32 and 32 are used, viz, 32 and 32, to avoid the expense of running a third line. The line wire 32 is, therefore, grounded at 54 so that its circuit may be completed through thei ground connection 55 at the generating en The two line circuits 32 and 32 are carrled respectively through coils 56 and 57 on two legs of the step-down transformer 53. They are then carried through two coils 58 on the third leg,-wound in such a direction that their resulting magnetic effect will react on the flux in this leg in co-operation with the flux in the other legs so that normal symmetrical three phase currents will be delivered by the transformer. These circuits 32 and 32 are then grounded at 44. Secondary coils 59?, 59 and 59 supply voltages to three single phase reactances 60, 60 and 60. Intermediate points of these wind- *ings 59, 59 and 59 are connected together by the conductor 61. The coils of the three phase reactance are connected to the three phase mains 62. Condensers are connected to the mains and to the ends of the secondary windings 59 59 and 59.

The operation of the unit net work 51 is similar to that of the network 50. The conductor 61 may be extended to constitute a neutral bus for the three phase system, which can then carry unbalanced load to advantage.

In Fig. 6, with balanced loads at 50, any one of the three single phase circuits acts as a return circuit for the two others and no separate return is required. If, however, a single circuit be used alone as in Fig. 8, some form of return circuit must be provided. This maybe secured by running a second wire back to the supply or by carrying the single wire around a cop to reach the startin int as shown in Fig. 7, or by usin the u iid as a return as in Fig. 8. In either fiie second or the last case but one line wire is required.

In Fig. 7 I have shown two single phase constant current circuits 34 and 34* similar to the circuits 32, 32 in Fi 6, these carrying currents 120 apart in p ase. I may obtain normal three phase voltage mains from these circuits as shown at 35, where the two circuits 34 and 34" are connected to two legs of a core type three phase transformer 36. In such a transformer the flux in any core is the resultant of the flux in the other two cores. If 34* and 34 are taken to two legs the fiux in the third will be the resultant of the fiuxes in the other two and will be substantially correct in phase and magnitude to furnish voltage for the third phase of a three phase system, as for example in the secondary windings, as 67, 67", 67, 68, 68", 680

I have shown two secondaries for each leg, one connected to the appropriate condenser 72, and the other to the appropriate reactance winding of the three hase reactance 71. The other ends of the windings 67, 67 67 are connected together by a conductor 69, and the other ends of the windings 68, 68*, 68, by the conductor 70. By this arrangement I increase the tendency for the circuits to maintain balanced conditions in the load mains 7 3. The arrangement of transformer secondary coils shown on the system 51, Fig. 6, may be used in place of the separated transformer coils, 67, 68, 67 68*, 67 and 68, this giving the same opportunity to secure a neutral bus bar and other advantages. This system is adapted more particularly to balanced loads. The separating. of the secondary windings of each phase of the stepdown transformer into two parts forces both the condenser and the reactance currents to equalize themselves, which is an inherent feature of true three phase quantities.

In Fig. 7, 7 3 and 7 3 are the generating networks which may be of the type of my invention but which may be of any other suitable type. The lines 34 and 34" make comlete circuits over the district where power is to be distributed, this rendering unnecessary any grounding to carry return currents, although either or both clrcuits 34: and 34 ma be grounded if desired.

Iii Fig. 8, represents a constant current circuit from any suitable source 43. A series of constant current devices 39, such as arc lamps are connected in the circuit and also at 38 a unit network of the type of my invention supplying constant potential mains 41. This circuit 40 is grounded at the gen erator as shown and at the end 42 remote from the generator and the earth acts as a return circuit.

current, substantially opposite in phase, ex-

cept for the in-phase component which in each case will represent the energy losses. I may vary this adjustment, however, where, by trial or otherwise, it is found that the operation is more suitable. It is ossible by making the condenser of somew at higher impedance than the reactance to secure a certain amount of compounding of the constant voltage or constant current.

In the case when the supply circuit is a constant potential circuit and the receiving circuit naturally a constant current circuit, there is a tendency to produce an excessive voltage, through resonance, should the receivin circuit become open-circuited. This excessive voltage may be held within safe limits by properly designing the core of the reactance so that it will oversaturate on excessive voltage, which will prevent extreme values, or by designing the condenser to have a larger impedance than the reactance, or the reactance to have a larger impedance than the condenser, which, also, will limit the rise of potential. Both of these results follow from the Equations 1 to 4 above. It is possible, at the same time such protection is secured, to obtain compounding of the current of a constant current receiving circuit or the potential of a constant potential receiving circuit by properly choosin the relativevalues of the condenser impe ance and the reactance impedance. When I, is zero in Fig. 1, with a constant value of E., the voltage E will be if n=.5. If the energy losses are zero and h =h E, will be infinite. If, however, k -.77z E.=2.8 h E By making the reactance impedance smaller than that of the condenser the sign of the compounding is reversed from the sign with a larger impedance and a similar change occurs with an interchange of load circuit and generator circuit, so that the advantages of compounding and protection against-excessive potential may he obtained at the same time.

I claim as my invention- 1. A network consisting of a reactance, a condenser and a transformer winding connected in a loop, in combination with a circuit connected across said loop and means for compounding the voltage in said circuit, said means consisting of connections between said circuit and an intermediate point of said ,windin to one side of the mid-point.

2. A con enser, a reactance and a transformer winding connected in a closed loop, in combination with a first circuit connected between the common point of the condenser and'the reactance and the transformer w1nding and a second circuit connectedin operative relation to said transformer winding together with means for modlfyin the relation between the voltage in the rst circuit and the current in the second circuit consisting of means for connecting the first c1 rcuit to a suitable intermediate po nt in said transformer winding.

3. In a network'consisting of a condenser, a reactance and a transformer winding connected in a closed loop, a work circuit and means for adapting the supply from said network to the natural voltage of the work circuit, said means consisting of homologous tap connections at intermediate points in said reactance and in said transformer Wind- E. A closed loop including a condenser, a reactance and a' transformer winding in series and a work circuit in combination with means for connecting said work circuit between an intermediate point in said reactance and an intermediate point in said transformer together with a supply circuit for said networ 5. In a system of distribution the combination of a three phase core type transformer, means for supplying constant currents in 120 phase relation to primary coils on two legs of said transformer, three secondary coils for said transformer, three reactance coils on a three branch core, three condensers, direct connections between said secondary windings, connections between said secondaries and the three condensers and connections from the secondary windings to the reactance coils, connections from the reactance coils to a work circuit, and from the condensers to the work circuit.

6. The combination of two conductors carrying constant currents diflering in phase, a transformer core containing three legs, coils on said legs and connections passin each of said constant currents through a coi on a separate leg and for passing both currents through separate coils on the third leg together with secondary windings 'on the three legs.

7. A unit network for interchanging constant current and constant potential three phase power consisting of a core type reactance having three legs, including three coils thereon, a condenser and a transformer windin in series, connected in shunt to each coil an connections for supply and receiving circuits.

8. In a system of electrical distribution, means for distributing constant potential energy from a suitable three phase source to a plurality of separated localities consisting of means for producing constant currents from two phases of said three phase constant potential source including a lurality of loops each consisting of a con enser, a reactance and a transformer winding in seriesmeans for transmitting said constant currents from said source to each of said localities and means for deriving three phase constant potential power from said constant currents at each of said localities including three condensers and three reactances connected to the receiving mains and three phase transformer secondaries connected to the reactances and the condensers and two transformer primaries'for said secondaries traversed by said constant currents.

9. A compounded system of distribution, comprising a closed loop, including a condenser and a reactance, and a transformer winding in series therein, the condenser and the reactance having impedances substan-' tially equal but with a certain predetermined degree of inequality, together with a constant potential and a constant current circuit connected therewith.

10. In a system ofelectrical distribution,

the combination with a plurality of local constant potential circuits and means at each local circuit for deriving constant potential current from current of constant strength, of a constant current supply and series connections between said supply and said local circuits. A

11. A three phase system of distribution" including three networks, each comprising a reactance, a condenser and a transformer winding in a closed loop, a three phase constant potential work circuit, a connection from each phase of the work circuit to the common connection point of a reactance and a condenser, a common connection between the middle points of said transformer windcircuit, the second secondary transformer coil being connected to one leg of said three legged reactance and of said three phase densers and for the threesecondaries feedwork circuit, together with a connection ing reactances. from the free ends of the condenser and re- Signed at New York in the county of 10 actance appropriate to each leg to one phase New York and State of New York this 6th 5 of the three phase WOlk circuit and a comday of August A. D. 1925."

mon connection for the free ends of the three transformer secondaries feeding con PERCY THGMAS. 

